Various types of labels are currently used to display names and information about contents on a glass bottle, a plastic bottle, and the like. Conventionally, paper labels, each of which is attached to an object by an adhesive, have been used. Recently, however, full wrapping labels are used in order to print a variety of contents or display a lot of information. For this reason, heat-shrinkable films have attracted considerable attention.
A heat-shrinkable film is referred to as a film which is contracted to an original state at a predetermined temperature or more after being stretched and oriented, and is used in packaging various shapes of containers.
A high-density polyethylene (HDPE) container is generally used for household supplies (e.g., shampoo, lotion, etc.), and is characterized in that it has a higher thermal expansion coefficient than those of other materials, and it starts to expand at 50° C. Owing to such characteristics of HDPE, when a conventional heat-shrinkable polyester film that starts to expand at 70° C. is used, the HDPE container starts to expand before the heat-shrinkable polyester film is contracted. As a result, this heat-shrinkable polyester film is labeled on the expanded HDPE container. However, when the temperature of the HDPE container labeled with the heat-shrinkable polyester film drops down to room temperature, the HDPE container contracts back to its original size, the film becomes loose, resulting in lose adhesivity of the heat-shrinkable polyester film to the HDPE container.
Therefore, it is required to develop a novel heat-shrinkable polyester film having excellent adhesivity when applied to a HDPE container.